Spark gap device for high-power electrical generators

ABSTRACT

The object of the invention is a high-voltage spark gap device operated in conjunction with a high-power electric generator and comprising an electric trigger system and at least two mutually spaced main electrodes. These main electrodes in particular are spheres and cooperate pairwise and face each other. This spark gap device furthermore comprises means to close the current loop and separated by a dielectric from the electrodes, said device being characterized in that the electric trigger system comprises as many trigger electrodes as there are main electrodes in it, said trigger electrodes being fitted with an insulating protector received in each main electrode of said device.

[0001] The present invention relates to the technical field of pulsed,high-power electrical generators and in particular to high-voltage sparkgap devices operating in conjunction with such generators.

[0002] Using spark gap devices with high-power electrical generators, aset of specific criteria is involved, among which foremost that of theirinductance which must be low in order to attain the shortest dischargetimes.

[0003] A number of designs already have been proposed in this field.

[0004] The monogap spark device is a gas spark-gap device consisting oftwo mutually opposite main electrodes. The trigger electrode isconfigured between the two main ones and when a high-amplitude pulse isapplied to this trigger electrode, it will create electrical paths inthe gases at regular time intervals under optimal conditions.

[0005] This spark gap device entails the drawback that its inherentgeometry precludes low inductances despite the formation of severalelectrical paths. Illustratively a spark gap device of this designentails a minimum inductance of about 20 nh.

[0006] Another spark gap device design already has been proposed. Thisis the surface spark gap. It operates substantially on the sameprinciple as the above described single gap spark gap devices, exceptthat the current paths follow the surface of a dielectric and hence aresituated closer to the current-loop closing means. Even if the latterentail a low and admissible inductance of about 5 nh, they still may notbe used for the high voltages that are fed from the high-voltagegenerators in conjunction with which the spark gap devices must operate.The main difficulty is to adjust the triggering system within the sparkgap device—when it can be done at all.

[0007] Lastly a third known spark gap device is the multiple spark gapdevice of low inductance wherein the charge voltage is spread acrossseveral gaps. In this design, a main electrode receives a voltage pulseand enables the closing of the gaps by capacitive coupling.

[0008] While the performance of this spark-gap device is fairlysatisfactory and it matches high-voltage generators, it doesnevertheless incur some drawbacks. In the first place a simple change inthe geometry of this spark gap device mandatorily entails making a newmold. As a result additional costs are caused by cold molding—which isan elaborate and uncertain procedure as noted by the high number ofmalfunctions of several series of spark gap devices of this kind. Also,to attain optimal operation, the trigger electrode must be molded into adielectric structure between the current paths and the current-loopclosing means. This feature is near mandatory and precludes moving thecurrent paths and the current-loop closing means nearer each other inorder to lower the spark gap device's inductance. Another drawback isthat the inductance of this spark gap device still is excessive and as aresult research into the electric arcs from the path generating mainelectrodes shows that not all the paths are initiated: when a first pathis formed, the voltage at the spark gap device terminals drops and mayaffect the closure of the other paths. Accordingly the observedinductance of about 10 to 15 nh of this spark gap device is too high toassure proper spark gap device operation when a high voltage is appliedto it.

[0009] The objective of the present invention is to remedy the abovedescribed drawbacks by proposing a high-voltage spark gap deviceallowing substantial reduction of its inductance so as to attaintriggering all arcing paths at each discharge, and to do so at very highvoltages.

[0010] Another objective of the present invention is to create areliable spark gap device making possible a mechanical designcircumventing molding the spark-gap device case and thus allowingflexibility when determining operational parameters such as gap size andnumber of arcing paths.

[0011] Lastly the purpose of the invention is improving high-powerelectric generator performance while reducing manufacturing costs bymeans of some product independence from the manufacturing process.

[0012] Accordingly the objective of the present invention is a spark gapdevice for a high-power electric generator, namely a high-voltage sparkgap device comprising an electric trigger system, furthermore twomutually spaced main electrodes in particular spheres, which operatepairwise and which are mutually oppositely situated, and current-loopclosing means that are separated by a dielectric from the mainelectrodes, said spark gap device being characterized in that theelectric trigger system is fitted with as many trigger electrodes asthere are main electrodes in the spark-gap device, said triggerelectrodes being fitted with a protective insulator and each beingreceived in a different spark-gap device main electrode.

[0013] Preferably the spark-gap device main electrodes are kept on thedielectric by means of slides.

[0014] The main electrodes are able to slide within these slides and canbe individually pressed against the dielectric by means such as springs.

[0015] In a preferred embodiment of the invention, the spark gap deviceis a high-voltage, multigap device operating in air at ambient or higherpressure, the gaps between the main electrodes being controlled byspacers.

[0016] The dielectric used in the spark gap device which is the objectof the present invention consists of thin insulating layers. Moreoverthe protective insulator of the trigger electrodes may be implemented bya high-voltage cable.

[0017] The invention offers the advantage of a high-voltage spark gapdevice of a design much simpler than those of the extant spark gapdevices. As a result such spark gap devices of the invention are moreeconomical.

[0018] Another advantage of the present invention is the improvement inperformance of the spark gap devices cooperating with high-powergenerators on account of reducing the spark-gap device inductance andthereby enabling closing all paths at each firing.

[0019] The invention is further discussed below in relation to theattached drawings.

[0020]FIG. 1 is a schematic cross-sectional sideview of part of thespark gap device of the invention fitted with two main electrodes,

[0021]FIG. 2 is a half cross-sectional sideview of a spark gap device ofa particular embodiment of the invention, and

[0022]FIG. 3 is a sectional view along the plane defined by the line I-Iof FIG. 2.

[0023]FIGS. 1 through 3 show a high-voltage spark gap device to be usedwith a high-power electric generator.

[0024] The spark gap device of the invention may assume severalembodiment modes; this feature is one of the advantages of such a sparkgap device which may be matched to different applications by means ofdifferent numbers of gaps and paths.

[0025]FIG. 1 shows schematically part of the spark gap device of theinvention, comprising two main electrodes 3. Preferably these mainelectrodes 3 are spherical and mutually apart. They cooperate with eachother and subtend an electric path 5 between them. This path shall becreated using an electric trigger system 4, 6 comprising two triggerelectrodes 6. In general this system includes as many trigger electrodes6 as there are spherical main electrodes 3. These spherical mainelectrodes are fitted with insulating protection 4 preferably in theform of the sheath of a high-voltage cable. Each trigger electrode thenshall be received in a different spherical main electrode 3 in aone-to-one relationship of the trigger electrodes 4 to the sphericalmain electrodes 3. However the insertion of the trigger electrode intothe main electrodes of the spark gap device does not depend on the mainelectrode shape.

[0026] Accordingly the spark gap devices of the invention are coupledcapacitively, and such capacitive coupling initiating the spark-gapdevice triggering is implemented at the very inside of the sphericalmain electrode 3—no longer outside the main electrode as in the priorart.

[0027] These main electrodes 3 make contact with a dielectric 2 whichpreferably is composed of thin insulating layers that rest on means 1implementing the current-loop closing means. Such a configuration of thevarious components allows considerably reducing the spark-gap deviceinductance due to thinness of the insulator 2 between the mainelectrodes 3 and the current-loop closing means 1.

[0028] The width of the dielectric 2 was reduced not only because thetrigger electrode 6 was integrated inside the main electrodes 3 but alsobecause using a set of such fasteners holding the main electrodesagainst the dielectric which do not require molding them into thedielectric. These diverse steps contributed substantially to move themain electrodes 3 closer to the current loop closing means 1 and henceto reduce the spark gap inductance to assure said spark gap's improvedoperation.

[0029] With respect to FIGS. 2 and 3, the spark gap device of theinvention may comprise a number of electric paths 5 and a number ofdifferent gaps depending on the application of said device. Theparticular configuration of the multi-path and multi-gap spark device 7of FIGS. 2 and 3 is merely illustrative. This spark gap device 7comprises twenty-two paths 5 and seven gaps. It comprises asubstantially parallelipipedic and hollow framework 12, its longitudinalside walls 13 being covered on their inside by current loop closingmeans 1. These current loop closing means 1 in turn are covered by thedielectric 2 which shall receive a contacting set of main electrodes 3on each side wall, said set of main electrodes 3 being divided into twosub-sets (only one being shown in FIG. 2). Accordingly these sub-setscomprise a given number of main electrodes each of which is affixed toone of the slides 8 which preferably are made of polyvinyl chloride andconfigured to be mutually parallel, comprising as many fasteners for themain electrodes 3 as there are desired paths to be initiated from thosemain electrodes on a given slide. Said slides furthermore may also bemade of another commonplace solid dielectric material such aspolyethylene, polycarbonate, polyurethane, depending on the environmentto which the material shall be exposed.

[0030] Illustratively the spark gap device of FIG. 2 shows slides 8fitted with six fasteners each receiving a main electrode 3 which isable to cooperate with another mutually opposite main electrode 3 andspaced from it by a gap. This inter-electrode gap is controlled by aspacer 10 preferably made of polyvinyl chloride and situated between twoconsecutive slides. Again as with the slides, said spacers as may bemade of another solid, commonplace dielectric materials if the spark gapdevice shall be exposed to a particular environment. The number of gapsis determined by the desired number of slides plus one.

[0031] The sets of slides and spacers or the like in this manner makesit possible to manufacture a spark gap device of simple and easilyvaried design. Merely changing the number of fasteners and the spacerwidths defining the gap suffices to match the spark gap device to theuser's needs.

[0032] As already specified above, the main electrodes 3 are forced bymeans of springs 9 or the like against the dielectric 2 which preferablyconsists of thin insulating layers. Such means 9 therefore allowapplying pressure on each main electrode 3 toward the outside of theframe 12 and against the dielectric 2. In this manner the mainelectrodes may slide within the fasteners of the slide 8 until theyshall make contact with the dielectric 2.

[0033] Be it borne in mind that when operating such a spark gapdevice—of which the trigger electrode 6 also may be in the form of arigid tube that is enclosed by an arbitrary insulator and that at thesame time assures the function of support on the frame 12—more desirableresults are attained with respect to the spark gap device's inductance:its inductance for a design containing 22 electric paths and 7 gapsremains below 5 nh, and consequently during each firing, all electricpaths are observed being closed.

[0034] By selecting the number of gaps, the spark gap device may beoperated in air at atmospheric pressure, and as a result both saiddevice and its design are even more simplified. However this kind ofspark gap device also operates very well at higher pressures.

[0035] Obviously various modifications may be introduced by the expertin the above described spark gap device which was discussed in merelyillustrative manner, without implying restriction and without therebytranscending the scope of the invention.

1. A spark gap device (7) for a high-power electric generator, saiddevice being designed for high voltages and comprising an electrictrigger system (4, 6) , furthermore at least two mutually spaced mainelectrodes (3) which in particular 5 are spheres and cooperate pairwise,and means (1) to close the current loop that are separated by adielectric (2) from the main electrodes, characterized in that theelectric trigger system (4, 6) comprises as many trigger 10 electrodes(6) as there are main electrodes (3) in the spark gap device, saidtrigger electrodes (4) being fitted with a protective insulator (4) andeach being received in a different main electrode (3) of the spark gapdevice.
 2. Spark gap device (7) for a high-power electric generator asclaimed in claim 2, characterized in that the spark gap device s mainelectrodes (3) are kept in place on the dielectric (2) by means ofslides (8).
 3. A spark gap device for a high-power electric generator asclaimed in claim 2, characterized in that the main electrodes (3) mayslide in the slides (8) and may be individually forced by means (9) suchas springs against the dielectric (2).
 4. A spark gap device for ahigh-power electric generator as claimed in any of the above claims,characterized in that said device (7) is a high-voltage, multi-gap sparkdevice operating in air at atmospheric pressure or at higher pressure,the gap between the main electrodes being controlled by a spacer (10).5. A spark gap device (7) for a high-power electric generator as claimedin any of the above claims, characterized in that the dielectric (2)consists of thin insulating layers.
 6. A spark gap device (7) for ahigh-power electric generator as claimed in any of the above claims,characterized in that the protecting insulator (4) is provided by ahigh-voltage cable.
 7. A spark gap device for a high-power electricgenerator as claimed in any of the above claims, characterized in thatthe trigger electrode (6) is a rigid tube.